1. Field of the Invention
The present invention relates to an optical interferometric measuring instrument, and more particularly to the ultra precision laser interferometric measuring instrument using laser light. Further, the present invention relates to a laser interference apparatus, and more particularly to the laser interference apparatus which processes an object disposed on a slider potion whose amount of movement is measured by a laser interferometric measuring instrument.
2. Related Art
In recent years, concerning the measurement of length, particular importance has come to be attached to the traceability of the length, and the presentation of the uncertainty of measurement accuracy has come to be required. In the present situation in which the laser wavelength serves as a standard of the length, a laser interferometric measuring system is widely used as a length measuring means in measuring instruments and apparatus, an ultra precision machining apparatus, and the like so as to facilitate the traceability of the standard of the length and simplify factors for the uncertainty of the measurement accuracy.
In the case where the laser interferometric measuring system is used as the means for measuring with high accuracy the displacement of a slider in the measuring instruments and apparatus, an ultra precision machining apparatus, and the like, variations of the laser wavelength ascribable to the change of the refractive index due to changes in the air temperature or pressure, humidity, and CO2 concentration in the atmosphere hamper the high-precision length measurement, so that it has been proposed to evacuate the optical path of the laser.
FIG. 7 shows the configuration of a conventional optical interferometric measuring instrument. This optical interferometric measuring instrument is comprised of a body base 710, a laser light source 712, an interferometer portion 714, a slider 716, a slider driving mechanism 718, a reflecting mirror 720, and a bellows 722.
The laser light source 712 is fixed on the body base 710, and is adapted to emit laser light for length measurement toward the reflecting mirror 720.
The interferometer portion 714 has a half mirror and the like, and is adapted to measure the distance to the reflecting mirror 720, i.e., the distance to an end portion of the slider 716, by detecting the phase difference between the direct light emitted from the laser light source 712 and the reflected light returned after being reflected by the reflecting mirror 720 after passing through the bellows 722.
The slider 716 is disposed on the body base 710, and is provided movably in the directions of arrows in the drawing by the slider driving mechanism 718. In a case where the length of an object to be measured is measured, the slider 716 is moved so as to allow an end portion of the slider 716 to abut against the object to be measured.
The reflecting mirror 720 is disposed at the end portion of the slider 716, and moves in the directions of arrows in the drawing in conjunction with the movement of the slider 716. Then, reflecting mirror 720 reflects the light emitted from the laser light source 712, and returns the laser light to the interferometer portion 714.
The bellows 722 functions as a light guiding portion for guiding the laser light from the laser light source 712 to the reflecting mirror 720, and one end thereof is connected to the interferometer portion 714, while the other end thereof is connected to the reflecting mirror 720. The bellows 722 is stretchable in the moving direction of the slider 716, and if the slider 716 is moved to measure the length of the object to be measured, the bellows 722 is also extended or contracted in conjunction with the movement of the slider 716. The interior of the bellows is exhausted of the air by a vacuum pump until it is set substantially in a vacuum state. Since the laser light from the laser light source 712 passes through the vacuum in the bellows 722, the length-measuring optical path is constantly kept in a vacuum state. Accordingly, the variation of the laser wavelength ascribable to a change in the refractive index due to changes in the air temperature, atmospheric pressure, humidity, and the CO2 concentration does not occur, so that high-accuracy measurement becomes possible.
However, there has been a problem in that the couple of forces consisting of the product of, on the one hand, an offset distance of an axis of a force combining a suction force of the bellows 722 attributable to the difference between the internal pressure (a vacuum state) of the vacuum bellows 722 and the atmospheric pressure and a spring force consisting of the product of a spring constant peculiar to the bellows 722 and its amount of extension and contraction and, on the other hand, an offset distance of a driving axis for moving the slider causes a change in the geometric attitude of the slider 716 and a change in its velocity during driving (these cause a positional change of the reflecting mirror 720) as well as a strain in the interferometer portion 714, thereby rendering the high-accuracy length measurement difficult.
FIG. 8 shows another configuration of the conventional optical interferometric measuring instrument. The difference with the optical interferometric measuring instrument shown in FIG. 7 lies in that, instead of the bellows 722, a bellows 824 having a double structure which is composed of an inner shell 824a and an outer shell 824b is provided as the light guiding portion. The inner side of the bellow 824 of the double structure (or an inside of the inner shell 824a) is exhausted of the air into a vacuum state by the vacuum pump in the same way as in FIG. 7, and the outer side (a space between the inner shell 824a and the outer shell 824b) is set to an appropriate pressure higher than the atmospheric pressure. Since the inner side of the bellows 824 is in a vacuum state, a suction force due to the difference with the atmospheric pressure occurs, but since the outer side of the bellows 824 is set to the pressure higher than the atmospheric pressure, an expanding force (force acting in an expanding direction) is conversely applied due to the difference with the atmospheric pressure. Accordingly, by using such a bellows 824 of the double structure, the suction force on the inner side which is in the vacuum state can be offset by the force consisting of the product of the appropriate pressure set on the outer side and the pressure receiving area in the extending and contracting direction.
It should be noted that the arrangements of the bellows 822 and 824 which are used in FIGS. 7 and 8 are as shown in FIGS. 9A-B, for example. The bellows 722 and 824 are each formed by superposing a plurality of doughnut-shaped weldable metallic plates 925 (e.g., made of austenitic stainless steel) shown in FIG. 9A and by welding them. FIG. 9B shows a vertical cross section of the bellows 722 and 824, and by bending and mutually welding the doughnut-shaped weldable metallic plates 925 shown in FIG. 9A, it is possible to obtain a member which has a hollow portion in its interior and which is stretchable in the directions of arrows. It goes without saying that a metal formed bellows is also used in addition to the welded bellows.
However, also in the case of the optical interferometric measuring instrument using the bellows 824 having the double structure shown in FIG. 8, the bellows 824 extends or contracts in conjunction with the movement of the slider 816, so that there has been a problem in that a change in the geometric attitude of the slider 816 and a change in its velocity during driving as well as a strain in the interferometer portion 814 still occur due to the force consisting of the product of the spring constant peculiar to the double-structure bellows 824 and the amount of its extension or contraction in the same case of FIG. 7, thereby rendering high-accuracy length measurement difficult.
It is, of course, conceivable to adopt a method in which the variation of the set pressures on the outer and inner sides due to the extension or contraction of the double-structure bellows as well as the force occurring in the extending or contracting direction of the bellows 824 due to the spring constant of the double-structure bellows 824 are detected by a sensor the like, so as to dynamically control the set pressures for the outer and inner sides. However, there occurs the problem that the a control system for the length measuring apparatus becomes complicated, and there is also a problem in that it is difficult to fabricate a double-structure bellows which is applicable over the entire length of the driving stroke of the slider 816, thereby leading to an increased cost.
Further, as a problem which is common to both the optical interferometric measuring instrumentes shown in FIGS. 7 and 8, there is a problem in that the longitudinal wave accompanied by the nonuniformity of the extension and contraction of the bellows occurring during the driving of the slider 716, 816 constitutes a disturbance in the attitude control or motion control of the slider 716, 816, thereby rendering high-accuracy length measurement difficult.
The invention has been devised in view of the above-described problems of the conventional art, and its first object is to provide an optical interferometric measuring instrument which is capable of reliably preventing a geometric change in the attitude of the slider and a change in its velocity during driving as well as a strain in the interferometer portion due to the force caused by the extension or contraction of the light guiding portion as a consequence of the movement of the slider, and which renders high-accuracy length measurement possible.
Further, its second object is to provide a laser interference apparatus which is capable of high-accuracy processing using a laser interferometric measuring instrument and which is capable of simply eliminating an error due to the thermal deformation of the body base caused by the variation of the ambient temperature and due to the deflection of the body base as a consequence of the movement of the slider.
To attain the above first object, in accordance with an optical interferometric measuring instrument of the invention, there is provided an optical interferometric measuring instrument including a laser light source, a light guiding portion whose interior is evacuated, a reflecting optical system disposed at one end of the light guiding portion and adapted to move with a slider, and a light interference system disposed at another end of the light guiding portion, a vacuum space between the light interference system and the reflecting optical system constituting an optical path for length measurement by laser light from the laser light source, characterized in that a moving portion and a light-guiding-portion fixing portion which move in interlocking relation to the slider are disposed in the length-measuring optical path, and the light guiding portion is disposed between the moving portion and the light-guiding-portion fixing portion, and includes a main light guiding portion disposed between the moving portion and the fixed portion and capable of freely extending and contracting in the moving direction of the slider, a first auxiliary light guiding portion disposed between the reflecting optical system and the moving portion and capable of freely extending and contracting in the moving direction of the slider, and a second auxiliary light guiding portion disposed between the fixed portion and the light interference system.
In the above-mentioned optical interferometric measuring instrument, it is preferable that the first auxiliary light guiding portion has a double structure, and is structured such that a vacuum interior thereof is covered with an outer shell having a predetermined pressure higher than the atmospheric pressure.
Further, in the optical interferometric measuring instrument, it is preferable that each of the first auxiliary light guiding portion and the second auxiliary light guiding portion has a double structure, and is structured such that a vacuum interior thereof is covered with an outer shell having a predetermined pressure higher than the atmospheric pressure.
In addition, in the above-mentioned optical interferometric measuring instrument, it is preferable that each of the main light guiding portion, the first auxiliary light guiding portion, and the second auxiliary light guiding portion has a double structure, and is structured such that a vacuum interior thereof is covered with an outer shell having a predetermined pressure higher than the atmospheric pressure.
To attain the above second object, in accordance with the invention there is provided a laser interference apparatus including a slider on which an object is fixed; a laser interferometer having a reference optical path and adapted to measure an amount of movement of a slider by using interference of laser light between the reference optical path and a variable-length optical path; and processing means fixed on a body base of the laser interferometer and adapted to process the object to be processed, wherein the object to be processed is processed by the processing means by using as a reference the amount of movement of the slider identified by the laser interferometer, characterized in that an optical axis of the laser interferometer and a point of processing the object to be processed by the processing means are disposed on a straight line, and that a fixed reflecting mirror for forming the reference optical path of the laser light is fixed on the body base so as to be located at an identical position to the point of processing in a direction of a moving axis of the slider, and both the variable-length optical path and the reference optical path extend in the moving direction of the slider on the body base.
In the above-mentioned laser interference apparatus, it is preferable that an interferometer portion, the reference optical path, and the variable-length optical path which make up the laser interference apparatus are in a vacuum state. Here, preferably, the reference optical path includes a pipe-like structure and a double-structure bellows, and is connected to the fixed reflecting mirror through the bellows.
Further, in the laser interference apparatus, it is preferable that the processing means and the fixed reflecting mirror are disposed on abridge structure straddling the slider, and the bridge structure is fixed to the body base.
In addition, in the laser interference apparatus, preferably, the object to be processed is a line standard having a scale fixed in parallel with a moving direction of the slider, and the processing means is a detector for detecting the scale at the point of processing.